Dielectric behaviour of dysprosium oxide films

The dielectric properties of vacuum-deposited dysprosium oxide films have been studied in the audio-frequency range (10²–10⁴ Hz) at various temperatures (78–373 K). The dielectric constant (6.7) was independent of film thickness for thicker films (d > 1000 Å). The capacitance was dependent both on temperature and frequency, but became constant for all frequencies at low temperature. Tan δ showed a frequency minimum and its variation with frequency and temperature was in agreement with the model proposed earlier by Goswami and Goswami. The breakdown field (≌10⁶ V cm^-1) followed the Forlani-Minnaja relation. The activation energy and the refractive index of these films were also measured.     

Fabrication of Al/MgO/C and C/MgO/InSe/C tunneling barriers for tunable negative resistance and negative capacitance applications

In this work, the design and characterization of magnesium oxide based tunneling diodes which are produced on Al and InSe films as rectifying substrates are investigated. It was found that when Al thin films are used, the device exhibit tunneling diode behavior of sharp valley at 0.15 V and peak to valley current ratio (PVCR) of 11.4. In addition, the capacitance spectra of the Al/MgO/C device show a resonance peak of negative capacitance (NC) values at 44.7 MHz. The capacitance and resistance–voltage characteristics handled at an ac signal frequency of 100 MHz reflected a build in voltage (V_bi) of 1.29 V and a negative resistance (NR) effect above 2.05 V. This device quality factor (Q)–voltage response is ~10⁴. When the Al substrate is replaced by InSe thin film, the tunneling diode valley appeared at 1.1 V. In addition, the PVCR, NR range, NC resonance peak, Q and V_bi are found to be 135, 0.94–2.24 and 39.0 MHz, ~10⁵ and 1.34 V, respectively. Due to the wide differential negative resistance and capacitance voltage ranges and due to the response of the C/MgO/InSe/C device at 1.0 GHz, these devices appear to be suitable for applications as frequency mixers, amplifiers, and monostable–bistable circuit elements (MOBILE).     

Structural and electrical properties of chromium and nickel films evaporated in the presence of oxygen

Electron-optical investigations of Cr films evaporated in the presence of oxygen (1 × 10^-7 to 5 × 10^-7 torr) have shown that the negative temperature coefficient of resistivity (TCR) is caused by small amounts of an amorphous oxide. On annealing these films in a vacuum of better than 5 × 10^-9 torr (e.g. for 140 h at 395°C) the amorphous phase crystallized and could be identified as Cr₂O₃. When Ni is evaporated in the presence of oxygen the TCR changes from positive to negative values at about 5 × 10^-5 torr. Since the negative TCR of oxygen-doped Cr-Ni (60/40) films did not change after annealing these films in a hydrogen atmosphere at 300°C (reduction of Ni oxide) it becomes plausible that the negative TCR of the Cr-Ni films, too, is caused by an amorphous Cr oxide surrounding the metal crystals.     

Dielectric properties of YSZ high-k thin films fabricated at low temperature by pulsed laser deposition

Yttria-stabilized zirconia (YSZ) films were deposited on Pt-coated silicon substrates and directly on n-type Si substrates, respectively, by pulsed laser deposition (PLD) technique using a YSZ (5 mol% Y₂O₃-stabilized ZrO₂) ceramic target. The YSZ films were deposited in 1.5×10⁻² Pa O₂ ambient at 300 °C and in situ post-annealed at 400 °C. X-ray diffraction (XRD) and differential thermal analysis measurements demonstrated that YSZ remained amorphous. The dielectric constant of amorphous YSZ was determined to be about 26.4 by measuring Pt/YSZ/Pt capacitor structure. The 6-nm-thick amorphous YSZ films with an equivalent oxide thickness (EOT) of 1.46 nm and a low leakage current of 7.58×10⁻⁵ A/cm² at 1 V gate voltage exhibit good electrical properties. YSZ thin films fabricated at low temperature 300 °C have satisfactory dielectric properties and could be a candidate of high-k gate dielectrics.     

Electrical properties of R-phycoerythrin containing Ag<Superscript>0</Superscript> nanoparticles in its channels

The electrical properties of R-phycoerythrin modified with Ag⁰ nanoparticles (Ag⁰ ? R-PE) as a candidate material for biosensors were studied were studied. Modification was ensured by a known procedure: synthesis of Ag⁰ nanoparticles in R-phycoerythrin channels through the addition of AgNO₃ to an aqueous R-phycoerythrin solution. According to electron microscopy results, the Ag⁰ ? R-PE contains predominantly elongated Ag⁰ nanoparticles 6.2 ± 0.5 nm in length, which form structures similar to rows 20–60 nm in length. The electrical conductivity, dielectric permittivity, and dielectric loss of the Ag⁰ ? R-PE have been measured in the frequency range from 0.01 Hz to 1 MHz. Filling the channels in R-phycoerythrin molecules with Ag⁰ nanoparticles has been shown to increase the alternating current electrical conductivity and dielectric loss of the material at low frequencies by more than 200 times and its dielectric permittivity by 40 times. Ag⁰ nanoparticles increase the direct current conductivity of R-phycoerythrin from 5 × 10^–14 to 2.5 × 10^–11 S/cm. The electrical properties of Ag ? R-PE are comparable to those of conductive polymer composites that contain metallic nanowires and are used in designing multifunctional films and smart materials.     

Surface morphology and electrical resistance of the oxide film on InSe

Experimental evidence is presented that air oxidation of InSe crystals produces a native oxide layer which possesses not dielectric but conductive properties and is separated from the semiconductor substrate by a potential barrier. The surface resistance of oxide films grown on InSe across and along the C axis has been measured as a function of oxidation time and temperature. The results demonstrate that the surface resistance of the films varies significantly only during the first five minutes of oxidation. Subsequently, the surface resistance remains almost constant at 100–150 Ω/□. The surface morphology of the native oxide on InSe has been studied by atomic force microscopy. The oxide surface is shown to be nanotextured due to nanospikes normal to the substrate surface. The influence of oxidation temperature and time on the dynamics of the surface morphology of the oxide layer (the lateral dimensions, height, and density of nanospikes) is examined.     

Synthesis of Large‐Area InSe Monolayers by Chemical Vapor Deposition

Recently, 2D materials of indium selenide (InSe) layers have attracted much attention from the scientific community due to their high mobility transport and fascinating physical properties. To date, reports on the synthesis of high‐quality and scalable InSe atomic films are limited. Here, a synthesis of InSe atomic layers by vapor phase selenization of In₂O₃ in a chemical vapor deposition (CVD) system, resulting in large‐area monolayer flakes or thin films, is reported. The atomic films are continuous and uniform over a large area of 1 × 1 cm², comprising of primarily InSe monolayers. Spectroscopic and microscopic measurements reveal the highly crystalline nature of the synthesized InSe monolayers. The ion‐gel‐gated field‐effect transistors based on CVD InSe monolayers exhibit n‐type channel behaviors, where the field effect electron mobility values can be up to ≈30 cm² V^?1 s^?1 along with an on/off current ratio, of >10⁴ at room temperature. In addition, the graphene can serve as a protection layer to prevent the oxidation between InSe and the ambient environment. Meanwhile, the synthesized InSe films can be transferred to arbitrary substrates, enabling the possibility of reassembly of various 2D materials into vertically stacked heterostructures, prompting research efforts to probe its characteristics and applications.     

Dielectric and optical properties of ZnS films

A.c. properties of ZnS film capacitors were studied at different temperatures (78 to 380 K) and frequencies (10² to 10⁵ Hz). Dielectric constant was found to be independent of frequency and film thickness (>900 Å). Capacitance, though dependent on temperature and frequency, became constant in a low temperature region for all frequencies. Loss factor, showing a pronounced minimum with frequency, increased with the rise of temperature and tan δ_min shifted to a higher frequency. Breakdown voltages were also measured.A proposed model of an equivalent circuit predicts some characteristic features of the capacitors which have been experimentally verified. Refractive indices of these films were measured for the visible region and the dielectric constant was evaluated for optical frequencies. Effects of substrate temperatures on these films were also studied.     

Dielectric properties of sol-gel derived Ta2O5 thin films

The dielectric constant and the dielectric loss of tantalum pentoxide (Ta₂O₅) thin films, produced by sol-gel spin-coated process on Corning glass substrates, have been investigated in the frequency range of 20-10⁵ Hz and the temperature range of 183-403 K, using ohmic Al electrodes. The frequency and temperature dependence of relaxation time has also been determined. The capacitance and loss factor were found to decrease with increasing frequency and increase with increasing temperature. The activation energy values were evaluated and a good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements were observed.     

Dielectric properties of Sr3CuNb2O9 perovskite ceramics

The dielectric constant ? and loss tangent tanδ of Sr₃CuNb₂O₉ perovskite ceramics prepared by solid-state reactions have been measured at temperatures from 300 to 900 K and frequencies from 25 to 1 × 10⁶ Hz. The results demonstrate that the samples slowly cooled from the temperature of the final, high-temperature firing (1200°C) have relatively low permittivity (? ? 10) and dielectric losses (tanδ ? 0.005 at 1 kHz) at room temperature, with no strong dielectric dispersion and no prominent maxima in the temperature dependences of their permittivity and dielectric loss. The ceramics quenched from 1300°C exhibit a pronounced Debye-type low-frequency relaxation and strong dielectric dispersion in conjunction with high permittivity ? ? 2000 at low frequencies and/or high temperatures. The observed dielectric anomalies in the Sr₃CuNb₂O₉ ceramics can be understood in terms of Maxwell-Wagner relaxation at dielectric inhomogeneities associated with the quenching-induced difference in oxygen-vacancy concentration between the grain bulk and surface layer.     

Dielectric losses and ac conductivity of Si–LiNbO3 heterostructures grown by the RF magnetron sputtering method

Single-axis <0001> textured polycrystalline LiNbO₃ films were grown on (001) Si substrates by the RF magnetron sputtering method. Dielectric losses that occur in the Si–LiNbO3 heterostructures are caused by the conductivity of the LiNbO3 films. Analysis of temperature and frequency dependence of ac conductivity in the frequency range f = 25/10⁵ Hz has demonstrated that it is expressed by the power law σ(ω) = Aω^s and is described in the framework of the correlated barrier-hopping model. Thermal annealing (TA) of the Si–LiNbO3 heterostructures causes an increase in the density of the localized states in the band gap of LiNbO3 from D = 7 × 10²⁴ m^?3 to D = 2 × 10²⁵ m^?3. The conduction mechanism is changed radically after TA and phonon-assisted tunneling influences ac conductivity at the frequency of up to 800 Hz. At high frequency (f > 800 Hz), dielectric relaxation predominates affecting frequency dependence σ(ω) on relaxation time τ = 6.6 × 10^?5 s.     

Frequency-dependent dielectric properties and electrical conductivity of CdIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

The real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity and ac conductivity (σ_ac) of CdIn₂S₄ single crystals (cubic structure) have been measured in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. In the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz, the ac conductivity of single-crystal CdIn₂S₄ follows the relation σ_ac ∼ f ^0.8, characteristic of hopping conduction through localized states near the Fermi level.     

Sol–gel deposited ceria thin films as gate dielectric for CMOS technology

In this work, cerium oxide thin films were prepared using cerium chloride heptahydrate, ethanol and citric acid as an additive by sol–gel spin-coating technique and further characterized to study the various properties. Chemical composition of deposited films has been analysed by FTIR which shows existence of CeO₂. The samples have been optically characterized using ellipsometry to find refractive index of 2·18 and physical thickness which is measured to be 5·56 nm. MOS capacitors were fabricated by depositing aluminum (Al) metal using the thermal evaporation technique on the top of CeO₂ thin films. Capacitance–voltage measurement was carried out to calculate the dielectric constant, flat-band voltage shift of 18·92, 0·3–0·5 V, respectively and conductance–voltage study was carried out to determine the D_it of 1·40 × 10¹³ eV^???1 cm^???2 at 1 MHz.     

Electrochemical properties of dielectric films of aluminium oxide deposited on silicon

Chemical, physical and some electrical properties of aluminium oxide dielectric films deposited on silicon substrates are reported. In the growth of these films we utilized the vapour phase reaction of the hydrolysis of aluminium trichloride (AlCl₃) in an r.f. heated horizontal reactor tube to give films of good thickness uniformity and run-to-run consistency. The activation energies associated with the constituent components of this complex chemical reaction were determined. It is shown that the films exhibit high dielectric constant (7.7±0.2) and field strength (in excess of 6 × 10⁶ V cm^?1) with low ionic content (typically anout 10¹⁰ cm^?2), making them an attractive contender for passivation and for use as the gate dielectric of metal-insulator-semiconductor (MIS) devices.     

Dielectric properties of NiO and NiO(Li)

The dielectric constant of NiO produced by the oxidation of Ni has been studied as a function of frequency up to 10⁸ Hz and of temperature from 300° to 550°K. The effect of Li doping on the dielectric constant has also been investigated. In addition, the behavior of the a.c. conductivity σ(ω) as a function of frequency ω has been determined up to 10⁸Hz and the loss tangent tan δ has been calculated. The results are interpreted on the basis of a non-adiabatic hopping mechanism at lower frequencies and an adiabatic hopping mechanism at higher frequencies. The dielectric breakdown field as a function of Li concentration has also been determined and is found to decrease exponentially with increasing Li concentration. In the NiNiONi structure, the capacitance is independent of the applied field up to fields of $\text{10}{}^5\text{V}\text{cm}$, and the resistivity is high up to fields of $\text{10}{}^5\text{V}\text{cm}$.     

Synthesis of SiOF nanoporous ultra low-k thin film

In this work, we have investigated the effect of annealing temperature on physical, chemical and electrical properties of Fluorine (F) incorporated porous SiO₂ xerogel low-k films. The SiO₂ xerogel thin films were prepared by sol–gel spin-on method using tetraethylorthosilicate as a source of Si. The hydrofluoric acid was used as a catalyst for the incorporation of F ion in the film matrix. The thickness and refractive index (RI) of the films were observed to be decreasing with increase in annealing temperature with minimum value 156 nm and 1.31 respectively for film annealed at 400 °C. Based on measured RI value, the 34 % porosity and 1.53 gm/cm³ density of the film annealed at 400 °C have been determined. The roughness of the films as a function of annealing temperature measured through AFM was found to be increased from 0.9 to 1.95 nm. The Electrical properties such as dielectric constant and leakage current density were evaluated with capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements of fabricated Al/SiO₂ xerogel/P–Si metal–insulator-semiconductor (MIS) structure. Film annealed at 400 °C, was observed to be with the lowest dielectric constant value (k = 2) and with the lowest leakage current (3.4 × 10^?8 A/cm²) with high dielectric breakdown.     

Understanding of post deposition annealing and substrate temperature effects on structural and electrical properties of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> MOS capacitor

The purpose of this study is to understand the effects of substrate temperature (ST) and post deposition annealing (PDA) on the structural-electrical properties of Gd₂O₃ film and to evaluate the electrical performances of the MOS based devices formed with this dielectric. The Gd₂O₃/Si structures were annealed at 500, 600, 700, and 800 °C under N₂ ambient after the films were grown on heated p-Si substrate at various temperatures ranged from 20 to 300 °C by RF magnetron sputtering. For any given ST, the crystallization/grain size increased with increasing PDA temperature. The bump in the accumulation region or continuous decrease in the capacitance values of the inversion region of the C–V curves for 800 °C PDA was not observed. The lowest effective oxide charge density (Q _eff ) value was obtained to be ??1.13?×?10¹¹ cm^?2 from the MOS capacitor with Gd₂O₃, which is grown on heated Si at 300 °C and annealed at 800 °C. The density of the interface states (D _it ) was found to be in the range of 0.84?×?10¹¹ to 1.50?×?10¹¹ eV^?1 cm^?2. The highest dielectric constant (ε) and barrier height \(({\Phi _B})\) values were found to be 14.46 and 3.68, which are obtained for 20 °C ST and 800 °C PDA. The results show that the negative charge trapping in the oxide layer is generally more than that of the positive, but, it is reverse of this situation at the interface. The leakage current density decreased after 20 °C ST, but no significant change was observed for other ST values.     

The chemical vapour deposition and characterization of ZrO2 films from organometallic compounds

ZrO₂ films were deposited on silicon substrates by oxygen-assisted decomposition of zirconium-β-diketonates at temperatures of 400–550°C. The deposits, fine-grained nearly stoichiometric monoclinic ZrO₂, were hard and showed strong adherence to the substrate. The films were characterized by transmission electron microscopy, X-ray diffraction and electron microprobe analysis and by measuring their dielectric and optical properties. The index of refraction was found to be 2.18, and the optical energy band gap was found to be 5.16 eV. The dielectric constant at 1 MHz was 17–18, and the dielectric strength varied between 1 × 10⁶ and 2.0 × 10⁶ V cm^?1. Capacitance-voltage measurements at 1 MHz indicated the presence of effective surface states with a concentration in the range (1.0?6.0) × 10¹¹cm^?2 for films deposited at temperatures above 500°C or for films deposited at 400–450°C and annealed at above 750°C. The flat-band voltages were between ?0.6 and + 0.2 V. The films showed satisfactory bias-temperature stability. The current-voltage characteristic followed an I ∝ V² dependence for negative bias and an I ∝ V^2.6 to I ∝ V^3.4 dependence for positive bias.     

Electrical behavior of Y-doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> thin films

Ba_0.6Sr_0.4TiO₃ (BST) and 1.5 at% Y-doped Ba_0.6Sr_0.4TiO₃ (Y-BST) thin films have been deposited on single-crystal (100) oriented LaAlO₃ substrates using pulsed-laser deposition technique (PLD), respectively. X-ray diffraction (XRD) scanning revealed that the two kinds of films could be epitaxially grown in pure single-oriented perovskite phases, but Y-BST thin films showed an enhanced crystallization effect. The dielectric properties of the pure and Y-BST thin films were measured at 10 kHz and 300 K with a parallel-plate capacitor configuration. The results revealed that the addition of Y as an acceptor doping is very effective to increase dielectric tunability, and to reduce leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 17.32 for BST to 25.84 for Y-BST under an applied electric field of 300 kV/cm. The leakage current density of the BST thin films at a negative bias field of 300 kV/cm decreases from 2.45 × 10⁻⁴ A/cm² to 1.55 × 10⁻⁶ A/cm² by Y doping. The obtained results indicated that the Y-doped BST thin film is a promising candidate material for tunable microwave devices.     

Dielectric properties of Al1.1Be0.6B22 crystals

The properties of single crystal samples of Al_1.1Be_0.6B₂₂, which are characterized by a large number of atoms per unit volume, have been studied at high (10¹³-10¹⁴ Hz) and low (10²-10⁵ Hz) frequencies. There is a considerable contribution to the polarizability of this compound due to a shift of the electron shells relative to the atomic nuclei. This accounts for large values of the refractive index—for example, 3.12 ± 0.05 at 0.64 μm—which is a record value for solids in the transparency range. At low frequencies, the dielectric characteristics are determined by the relatively high conductivity of the material, which represents an extrinsic p type semiconductor.